Impaired Driving Charges and Retrograde Analysis: When Time is an Element of a Crime

Unlike some crimes, impaired driving charges like DUI and drugged driving have an element of timing that any prosecutor must prove to obtain a conviction against an alleged drunk driver.

Under Pennsylvania's DUI statute, title 75 section 3802(a), subdivision (1), "general impairment" is defined as driving, operating or controlling a vehicle "after imbibing a sufficient amount of alcohol such that the individual is rendered incapable of safely driving...". An impaired driver can also be convicted under the "general impairment" subdivision if he or she drives, operates or otherwise controls a vehicle after a blood or breath test shows that the alcohol concentration in the bloodstream is at least 0.08% but less than 0.10%.

Similarly, under the impaired driving statutes for controlled substances, drivers may be charged with a crime if they operate a vehicle while any amount of a Schedule I, Schedule II or Schedule III substance or their metabolites in their blood streams.

Retrograde Analysis Used to Prove Intoxication Hours After Alleged DUI

But what do police do when they cannot test a driver for several hours after the driver operated a vehicle? Or what if police believe that a driver who tests under the limit of a certain offense may actually have been operating a vehicle with a much higher BAC? If these questions arise during the course of a DUI arrest, the driver's BAC may be analyzed using a process called retrograde extrapolation.

Retrograde extrapolation is a scientific test that is used to estimate the level of alcohol concentration (or other substances) in the bloodstream at an earlier time. Basically, analysts will use a test result taken at a certain time, then apply formulas to the test result to determine the BAC at the time a driver was allegedly operating a vehicle. Retrograde extrapolation is most often used when police arrest an alleged drunk driver, but do not obtain a BAC test result until more than two hours after the arrest.

According to the language in the DUI statutes, if police test a driver within two hours after the individual has driven, retrograde extrapolation is not used. If the driver has significant amounts of alcohol in his or her system, the driver will be charged under the "general impairment" statute, or with one of the enhanced DUI offenses. Thus, the prosecutor must only present evidence of the time the driver was driving and the time the test was taken, if within the two-hour period.

Once the two-hour period has elapsed, police usually must use retrograde extrapolation to show the driver's BAC at the time he or she was last operating a motor vehicle. But the Pennsylvania Supreme Court carved out an exception for drivers with extremely high BACs who are being prosecuted under the "general impairment" statute.

In Commonwealth v. Segida, 985 A.2d 871 (Pa. 2009), the Supreme Court was presented with a case where a driver had an extremely high BAC - .326%. The prosecutor did not present evidence that established the exact time that the driver last drove or the time that the BAC was tested at trial. The Supreme Court determined that the prosecutor can still show that the driver could not safely drive a vehicle because of impairment because the BAC was so high along with other evidence that the officer observed at the time of arrest including failed field sobriety tests, demeanor, slurred speech and other observations.

Metabolite Testing: Arrests for Drugged Driving Days After Consumption?

Another potentially absurd result of Pennsylvania's impaired driving statutes involves driving under the influence of a controlled substance. Unlike DUI, drivers suspected of drugged driving can be tested for any Schedule I, II, or III drug or any metabolite of those drugs. That is where the absurdity of the statute may come into play.

According to the National Highway and Traffic Safety Administration, marijuana metabolites generally will have a positive result within 1 to 3 days of consumption, but may appear in the bloodstream up to 5 weeks after ingesting marijuana. NHTSA reports that cocaine metabolites remain in the system for 2 to 4 days up to 10 days following a heavy binge. For methamphetamine, metabolites remain in the system for 1 to 4 days and up to a week for chronic users.

Any allegedly impaired driver tested for drugs and metabolites risks conviction for driving under the influence of a controlled substance days or even weeks after consumption of a controlled substance, regardless of whether the driver still felt the effects of the drug.

If you have been arrested or charged with an impaired driving offense in Pennsylvania, talk to an experienced DUI defense attorney as soon as possible. Time is not on your side.

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